1. Field of the Invention
The present invention is related to a server apparatus that is interposed in communications performed among a plurality of terminal apparatuses connected to each other via an IP network such as the Internet.
2. Description of the Related Art
Conventionally, for example, images photographed by indoor network cameras have been confirmed via the Internet from externally provided portable terminals (terminal apparatuses) (refer to, for example, patent publication 1). In such systems, the indoor network cameras are connected to routers, and the routers are connected to WANs (Wide Area Networks) such as the Internet. FIG. 17 shows one conventional system structural diagram of network terminals and network cameras.
As represented in FIG. 17, a global IP address (for example, 43.251.231.100) has been allocated as an IP address to a router, and at the same time, a private IP address (for example, 192.168.1.1) has been allocated to this router. Furthermore, private IP addresses have been allocated to network cameras under management by the above-described router. For example, in such a case that 3 sets of network cameras have been connected to the single router, as private IP addresses, “192.168.1.251” has been allocated to the first network camera; “192.168.1.252” has been allocated to the second network camera; and “192.168.1.253” has been allocated to the third network camera, respectively.
Then, within a WAN, when the above-described global IP address is used, this router can be identified. However, the network cameras under management of the router cannot be viewed from the side of the WAN. Conversely, in a LAN (Local Area Network) under management of this router, for example, the respective network cameras provided within the LAN can be accessed from a personal computer PC by utilizing the private IP addresses. However, the personal computer PC cannot access any network appliances provided on the side of the WAN by utilizing private IP addresses. As previously explained, within each of the WAN and the LAN, network appliances belonging to either the WAN or the LAN may be connected to each other by using either the global IP address or the private IP addresses. However, since there is no direct relationship between two IP addresses (namely, global IP address and private IP addresses), connections between both network appliances cannot be simply carried out. As a consequence, technical ideas such as the NAT (Network Address Translator) are necessarily required, which will be described later.
First of all, the reason why global IP addresses cannot be allocated to all of terminals in this case will now be described. The routing protocol of IP (Internet Protocol) under use in the Internet presently corresponds to the 32-bit IPv4, and since global IP addresses are utilized all over the world, these global IP addresses are under exhausted condition. In order to solve this exhausted condition, the 128-bit IPv6 has been proposed as the next generation global IP addresses. It takes more, or less time in order to transfer the 32-bit IPv4 to the 128-bit IPv6. In addition, considering such an aspect that security as to appliances provided in LANs when these appliances are connected to WANs can be easily secured and also these appliances can be easily operated, there are some merits in network systems operable based upon the protocol IPv4 by interposing routers. As a consequence, there are great possibilities that presently available connection modes of the routing protocol IPv4 may be utilized for the time being, so that IP terminal apparatuses such as network cameras may be effectively utilized until near future.
In such a case that an externally provided portable terminal accesses a network camera, the portable terminal can merely access only such a router to which a global IP address has been allocated, for instance, the global IP address of “43.251.231.100” in the above-explained example. In other words, the portable terminal cannot directly access the network camera. As a consequence, this portable terminal once accesses the above-described router to which the global IP address has been allocated, and thereafter, the portable terminal must request this router to be connected to the network camera.
As previously described, in such a case that a plurality of terminals have been connected to the router having the global IP address “43.251.231.100”, these plural terminals can be accessed from a portable terminal provided on the side of WAN by employing this commonly-used global IP address “43.251.231.100.” However, in order that the above-described portable terminal is connected to one terminal among the plurality of terminals connected to the router, by utilizing only the global IP address allocated to the router this terminal cannot be specified. Accordingly, this problem may be solved by furthermore applying a port number to the specific terminal, which is different from the global IP address.
For instance, with respect to the network camera having the private IP address “192.168.1.251” connected to the router, a port number “50002” is allocated thereto, as viewed from the WAN side; a port number “50001” is allocated to the network camera having the private IP address “192.168.1.252”; and another port number “5000” is allocated to the network camera having the private IP address “192.168.1.253.” Then, while the correspondence table with respect to the private IP addresses and the port numbers has been previously registered in the router, port forwarding operation is executed by referring to the correspondence table while utilizing a so-called “NAT (network Address Translator)”, or an IP masquerade equipped with a dynamic correspondence table.
As previously explained, the individual port numbers are allocated to the respective plural terminal apparatuses by utilizing either the NAT technique or the IP masquerade technique, and any one of these individual port numbers is utilized in combination with the global IP address commonly applied to the router. As a result, even when there is only one global IP address, any one of these plural terminal apparatuses under management of the router can be specified to be accessed.
However, in accordance with the above-described NAT technique, the same terminal apparatus (for example, same network camera) that is connected to the WAN cannot be simultaneously accessed by the plural terminal apparatuses provided within the LAN. This reason is given as follows: That is, with respect to communications between the router and the terminal apparatuses of the WAN, more than 1 session cannot be established. To the contrary, this problem may be dynamically solved if the IP masquerade technique is employed, so that the same terminal apparatus provided in the WAN can be simultaneously accessed from the plural terminal apparatuses. However, in this communication method based upon the IP masquerade technique, if such a connecting process that the terminal apparatus of the WAN side is firstly connected from the plurality of terminal apparatuses (namely, network cameras provided in LAN) connected to the router is not conducted, then the terminal apparatuses provided inside the LAN cannot be communicated with the terminal apparatus provided on the WAN side, while the connection is newly established.
A method for firstly starting a communication from the WAN side with respect to a network camera provided within a LAN by using the IP masquerade technique has not yet been proposed in the present stage. Although there are some possibilities that a server, or the like are initiated within a LAN, in order that the server provided in this LAN can be accessed from the WAN side, both a private IP address and a port number of this server must be previously registered in a correspondence table of the router by a user in a manual manner. In order to register these private IP address and port number in the correspondence table, the user firstly must know the IP address of the router, and also, the user is necessarily required to grasp an ID and a password, which are utilized so as to access the router. After the above-described initial condition has been established, the user accesses the router, and then, is required to enter the private IP address and the port number of the server, resulting in very cumbersome works. Also, when the server is accessed from the WAN side, the user must designate the global IP address of the router and the port number of the server, which also conducts a cumbersome work. Moreover, there are some possibilities that the global IP address of the router may be changed. As a consequence, if the global IP address of the router is changed, then the server cannot be accessed even when the old global IP address is used. Accordingly, certainty may be deteriorated.
Also, a communication relay apparatus has been proposed which is connected to such network connection appliances as a router and a gateway (Patent publication 2). However, a registration request must be transmitted from an IP terminal to the communication relay apparatus. The above-described registration request is constructed by employing a private address, a terminal name, a terminal attribute, a service name, a service attribute, a port number, and the like. Accordingly, this conventional communication relay apparatus has a similar problem to the above-described conventional technique (Patent publication 1).
As a consequence, the applicant of the present invention has also proposed the router capable of performing the dynamic forward setting operation based upon the UPnP standard (Patent publication 3). However, this conventional technique similarly constitute such a limited solution that the communicating operation may be merely carried out only via the router equipped with the dynamic port forward function of the UPnP standard.    Patent Publication 1: JP-A-2005-210583    Patent Publication 2: JP-A-2002-141953    Patent Publication 3: JP-A-2005-33250